I prefer Security for a few reasons.
First, they are defending the Ark’s founders from a bunch of unwelcome refugees. The fact that the founders even allowed 40K refugees to squat in a city that can only sustain 5K is a testament to their compassion (even if it was horribly short-sighted).
Also, and this is me being a bit selfish here, if I were to have to choose a side in real life the choice is obvious: Security has better equipment, they are well fed, they have access to clean drinking water, their weapons are well maintained, and they have greater access to the Ark’s resources, like the train.
Furthermore, while Security may be mowing down armed rebels, the Resistance resorts to mass murder of civilians twice (the surface to surface missile aimed at the tower and sabotaging the reactor).
Finally, I actually think it would be a mistake to contact the outside world. The Ark is overcrowded enough as it is, they don’t need to be alerting anyone else of its existence or location.
-JJ